The retainer for a tapered roller bearing is formed to a circular truncated cone shape as a whole, and includes a small annular section that faces the roller small end faces of tapered rollers, a large annular section that faces the roller large end faces of the tapered rollers, and retainer bar sections that partition the space between the small annular section and the large annular section into pockets. A resin retainer in which the small annular section, the large annular section, and all retainer bar sections (i.e., all pockets) are integrally injection molded is conventionally used.
To realize a simple mold structure from the standpoint of dimensional restriction that arises when obtaining a resin retainer for a tapered roller bearing and productivity, gates are arranged in a mold portion for molding the small annular section. Weld lines cannot be eliminated in the injection molding of the resin retainer. The weld lines are discontinuous portions of the material that are generated at the sites where the surfaces of injected resin portions merge at a low temperature. The mechanical strength is thus poor at such weld lines. Countermeasures have been taken to increase the sectional areas of the weld line generating sites as large as possible so that breakage does not occur from the regions of the weld lines (below-identified Japanese Patent Publication No. 2006-70926 A).